The copolymerization of ethylene and 1-hexene in the presence of a catalyst system comprised of the reaction product of a bis-hydrocarbylsilyl chromate and a trihydrocarbylaluminum compound has been disclosed. The latter compound is, on occasion, identified as a cocatalyst and, at other times, as a promoter or reducing agent when it is reacted with the chromate prior to carrying out the copolymerization. See, for example, U.S. Pat. Nos. 3,324,095; 3,324,101 and 3,704,287.
In some remote locations where 1-hexene is unavailable, there is a need for a simple process for making 1-hexene for use as a comonomer in quantities which are usually not sufficient to justify the expense of a separate plant for the trimerization of ethylene. Without such a process, copolymerization with the catalyst system described above is simply not economic.
An example of a trimerization process, which requires its own plant is the process described in U.S. Pat. No. 4,668,838, while an example of in situ dimerization/copolymerization can be found in U.S. Pat. No. 4,861,846. The latter patent describes a process, which provides comonomer in situ. Unfortunately, the comonomer is 1-butene. Further, the process utilizes both a polymerization catalyst and a dimerization catalyst.
It would be advantageous to provide an in situ trimerization/copolymerization process where the trimer is 1-hexene and only one catalyst is necessary for both the trimerization and copolymerization.